The teaser site's tag line reads, "M. Welcome to the next chapter." The now official X5 M and X6 M will certainly be something we've never read in the book of BMW high performance vehicles. Recent chapters have featured high-horsepower, rear-wheel-drive cars like the M3, M5 and M6 as their main protagonist, but these new Ms will be big, weigh over 5,000 lbs apiece and use all-wheel drive. In addition to the new teaser site that rounds up all available info on the two newest Ms, BMW has released a first official teaser video in which the M division's Bernd Limmer reveals that the X5 M and X6 M will be powered by versions of the existing twin-turbo 4.4L V8, likely tuned to around 500 horsepower. Being an M car has always required more than just high horses, however, and we can expect the X vehicles to feature heavily tuned suspensions and all-wheel-drive systems with a rear bias for better handling. Throw in better brakes, bigger wheels and tires and subtly revised styling, and consider the next chapter of M read until the official reveal takes place in early April. Follow the jump to watch BMW's official teaser for the X5 M and X6 M.